Mar 28, 2021 11:45 PM
Like magic: Physicists conjure curious quasiparticles
https://www.quantamagazine.org/like-magi...-20210324/
EXCERPTS: Quasiparticles are kind of particles. Barred entry from the exclusive club of 17 “fundamental” particles that are thought to be the building blocks of all material reality, quasiparticles emerge out of the complicated interactions between huge numbers of those fundamental particles. Physicists can take a solid, liquid or plasma made of a vast number of particles, subject it to extreme temperatures and pressures, and describe the resulting system as a few robust, particlelike entities. The emerging quasiparticles can be quite stable with well-defined properties like mass and charge.
Polarons, for instance, discovered by Lev Landau in 1933 and given a cameo on Star Trek: Voyager in 1995, materialize when many electrons are trapped inside a crystal. The push and pull between each electron and all the particles in its environment “dress” the electron so that it acts like a quasiparticle with a larger mass.
In other types of condensed matter that have dominated research over the last few decades, things get a whole lot weirder. Researchers can create quasiparticles that have a precise fraction of the electron’s charge or spin (a kind of intrinsic angular momentum). How these exotic properties emerge is still not understood. “It’s literally like magic,” said Sankar Das Sarma, a condensed matter physicist at the University of Maryland.
Using intuition, educated guesswork and computer simulations, condensed matter physicists have become better at figuring out which quasiparticles are theoretically possible. Meanwhile in the lab, as physicists push novel materials to new extremes, the quasiparticle zoo has grown quickly and become more and more exotic. “It really is a towering intellectual achievement,” said Natelson.
Recent discoveries include pi-tons, immovable fractons and warped wrinklons. “We now think about quasiparticles with properties that we never really dreamt of before,” said Steve Simon, a theoretical condensed matter physicist at the University of Oxford.
Here are a few of the most curious and potentially useful quasiparticles. [see article for list and details]
[...] The findings suggest that quasiparticles can be far more robust than researchers once thought. The line between particle and quasiparticle is becoming blurred. “I don’t see a fundamental difference,” Ruben Verresen said.
Quasiparticles arise out of arrangements of many particles. But what we term fundamental particles, such as quarks, photons and electrons, may not be as elementary as we think. Some physicists suspect that these apparently fundamental particles are emergent as well — though from what exactly, no one can say.
“We don’t know the fundamental theory from which electrons, photons and so on actually emerge. We believe there is some unifying framework,” said Leon Balents, a theorist who researches quantum states of matter at the University of California, Santa Barbara. “The things we think of as fundamental particles probably aren’t fundamental; they’re quasiparticles of some other theory.” (MORE - details)
RELATED: What is a particle? ..... Everything is made of fields
‘Time Is Elastic’
https://przekroj.pl/en/science/time-is-e...en-johnson
EXCERPTS: The differences were tiny, but the implications were massive: absolute time does not exist. For each clock in the world, and for each of us, time passes slightly differently. But even if time is passing at ever-fluctuating speeds throughout the universe, time is still passing in some kind of objective sense, right? Maybe not.
Physics without time. In his book "The Order of Time," Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.
So, why do we perceive time as flowing forward? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.
Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.
"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the Financial Times. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."
He continues: "Entropy growth orients time and permits the existence of traces of the past, and these permit the possibility of memories, which hold together our sense of identity. I suspect that what we call the "flowing" of time has to be understood by studying the structure of our brain rather than by studying physics: evolution has shaped our brain into a machine that feeds off memory in order to anticipate the future. This is what we are listening to when we listen to the passing of time. Understanding the "flowing" of time is therefore something that may pertain to neuroscience more than to fundamental physics. Searching for the explanation of the feeling of flow in physics might be a mistake."
Scientists still have much to learn about how we perceive time, and why time operates differently depending on the scale. But what's certain is that, outside of the realm of physics, our individual perception of time is also surprisingly elastic.
[...] It seems few scientists or philosophers believe time is completely an illusion. "What we call time is a rich, stratified concept; it has many layers," Rovelli told Physics Today. "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."
What is an illusion is the idea that time flows at an absolute rate. The river of time might be flowing forever forward, but it moves at different speeds, between people, and even within your own mind... (MORE - details)
https://www.quantamagazine.org/like-magi...-20210324/
EXCERPTS: Quasiparticles are kind of particles. Barred entry from the exclusive club of 17 “fundamental” particles that are thought to be the building blocks of all material reality, quasiparticles emerge out of the complicated interactions between huge numbers of those fundamental particles. Physicists can take a solid, liquid or plasma made of a vast number of particles, subject it to extreme temperatures and pressures, and describe the resulting system as a few robust, particlelike entities. The emerging quasiparticles can be quite stable with well-defined properties like mass and charge.
Polarons, for instance, discovered by Lev Landau in 1933 and given a cameo on Star Trek: Voyager in 1995, materialize when many electrons are trapped inside a crystal. The push and pull between each electron and all the particles in its environment “dress” the electron so that it acts like a quasiparticle with a larger mass.
In other types of condensed matter that have dominated research over the last few decades, things get a whole lot weirder. Researchers can create quasiparticles that have a precise fraction of the electron’s charge or spin (a kind of intrinsic angular momentum). How these exotic properties emerge is still not understood. “It’s literally like magic,” said Sankar Das Sarma, a condensed matter physicist at the University of Maryland.
Using intuition, educated guesswork and computer simulations, condensed matter physicists have become better at figuring out which quasiparticles are theoretically possible. Meanwhile in the lab, as physicists push novel materials to new extremes, the quasiparticle zoo has grown quickly and become more and more exotic. “It really is a towering intellectual achievement,” said Natelson.
Recent discoveries include pi-tons, immovable fractons and warped wrinklons. “We now think about quasiparticles with properties that we never really dreamt of before,” said Steve Simon, a theoretical condensed matter physicist at the University of Oxford.
Here are a few of the most curious and potentially useful quasiparticles. [see article for list and details]
[...] The findings suggest that quasiparticles can be far more robust than researchers once thought. The line between particle and quasiparticle is becoming blurred. “I don’t see a fundamental difference,” Ruben Verresen said.
Quasiparticles arise out of arrangements of many particles. But what we term fundamental particles, such as quarks, photons and electrons, may not be as elementary as we think. Some physicists suspect that these apparently fundamental particles are emergent as well — though from what exactly, no one can say.
“We don’t know the fundamental theory from which electrons, photons and so on actually emerge. We believe there is some unifying framework,” said Leon Balents, a theorist who researches quantum states of matter at the University of California, Santa Barbara. “The things we think of as fundamental particles probably aren’t fundamental; they’re quasiparticles of some other theory.” (MORE - details)
RELATED: What is a particle? ..... Everything is made of fields
‘Time Is Elastic’
https://przekroj.pl/en/science/time-is-e...en-johnson
EXCERPTS: The differences were tiny, but the implications were massive: absolute time does not exist. For each clock in the world, and for each of us, time passes slightly differently. But even if time is passing at ever-fluctuating speeds throughout the universe, time is still passing in some kind of objective sense, right? Maybe not.
Physics without time. In his book "The Order of Time," Italian theoretical physicist Carlo Rovelli suggests that our perception of time — our sense that time is forever flowing forward — could be a highly subjective projection. After all, when you look at reality on the smallest scale (using equations of quantum gravity, at least), time vanishes.
So, why do we perceive time as flowing forward? Rovelli notes that, although time disappears on extremely small scales, we still obviously perceive events occur sequentially in reality. In other words, we observe entropy: Order changing into disorder; an egg cracking and getting scrambled.
Rovelli says key aspects of time are described by the second law of thermodynamics, which states that heat always passes from hot to cold. This is a one-way street. For example, an ice cube melts into a hot cup of tea, never the reverse. Rovelli suggests a similar phenomenon might explain why we're only able to perceive the past and not the future.
"Any time the future is definitely distinguishable from the past, there is something like heat involved," Rovelli wrote for the Financial Times. "Thermodynamics traces the direction of time to something called the 'low entropy of the past', a still mysterious phenomenon on which discussions rage."
He continues: "Entropy growth orients time and permits the existence of traces of the past, and these permit the possibility of memories, which hold together our sense of identity. I suspect that what we call the "flowing" of time has to be understood by studying the structure of our brain rather than by studying physics: evolution has shaped our brain into a machine that feeds off memory in order to anticipate the future. This is what we are listening to when we listen to the passing of time. Understanding the "flowing" of time is therefore something that may pertain to neuroscience more than to fundamental physics. Searching for the explanation of the feeling of flow in physics might be a mistake."
Scientists still have much to learn about how we perceive time, and why time operates differently depending on the scale. But what's certain is that, outside of the realm of physics, our individual perception of time is also surprisingly elastic.
[...] It seems few scientists or philosophers believe time is completely an illusion. "What we call time is a rich, stratified concept; it has many layers," Rovelli told Physics Today. "Some of time's layers apply only at limited scales within limited domains. This does not make them illusions."
What is an illusion is the idea that time flows at an absolute rate. The river of time might be flowing forever forward, but it moves at different speeds, between people, and even within your own mind... (MORE - details)